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Wind Farms: Do they kill birds?

A short while ago I read this shocking and disturbing article about bird deaths from wind farms on I immediately asked myself: "Is that really true?" I wanted to know the right answer to this question, whether or not I liked it. If we want to create a peace legacy for future generations, to safeguard the planet for both humans and our non-human friends, we need to know the truth.

The issue is this: the story above claims that millions of birds are killed by wind farms. But a "green" friend I mentioned this to told me that this is absurd: she had studied wind farms in depth, she had personally visited them, and they were the safest, most wildlife-friendly places imaginable; the blades rotate so sedately nothing could possibly be killed by them; and there wasn't a dead or injured bird to be found anywhere around about. She went so far as to wonder if the writers of the above article weren't simply lying through their teeth.

The paradox I was struggling with was this: my green friend is without doubt one of the most truthful people I know. I did not doubt her account for a second. Equally, it seemed impossible that anyone could write such a credible-sounding article as the one linked above. Two truthful sources in direct contradiction - I needed facts that no one could dispute, because if lies are involved (and who won't at least wonder about the possibility?), it isn't good enough to merely discover the truth; I also needed it in a form that would allow anyone to prove it for themselves.So here's what I did.

First, I guessed the answer to the question. Then, I went to authoritative web sites that have a vested interest in my guess being wrong. Why? If my guess is wrong, such sites will have the evidence to show it. I shouldn't uncritically accept such data, but on the other hand, any data they provide that vindicates my guess will be the most credible I have within my power to obtain. Short of actually mounting a massive raw-data investigation of my own (visit wind farms, search for birds, and so on - which I can't afford to do), I cannot be more certain. And since I want to help you to answer the question for yourself as well, only data from an authoritative source will help you.

I could have guessed either way, but I guessed that wind farms do indeed kill lots of birds. Why? Firstly, the link above gives lots of bare facts that can be checked (such as a death toll of over a million per year in Germany alone), whereas my friend's assertions about not finding dead birds is much harder to directly investigate. But the method is sound either way. If the guess is wrong, I'll find evidence of it, then I can reverse my guess and go looking the other direction.

So I started at the European Environment Agency. If they can't be counted as authoritative, enthusiastic supporters of wind farms, I don't know who can. And Lo! I found an official report on their website: "Europe's onshore and offshore wind energy potential". On page 71 there is an appendix about animal deaths.

The first thing I think genuine wildlife and environment lovers need to note about this is the title they give to the section: "Introduction to environmental and social constraints". Why? Well I don't know about you, but animals suffering and dying is not my idea of a "constraint". It is a tragedy. In large numbers or small.

Moving on then. After some not-unexpected patter about saving the planet, the opening paragraph gives us: "The challenge is thus to meet the wind energy targets in a way that minimises the negative impact on biodiversity."

It seems that my and the EEA's attitudes to animal suffering are worlds apart. I don't need (and again, I don't speak for others) a species to be in danger or "biodiversity" to be threatened to be seriously disturbed by animal suffering. And I want to see it discussed openly, not hidden underneath euphemisms like "negative impact". If you love animals, I recommend you download this report and read this section in its entirety. My take: one of the most cruel-hearted, icy, disengaged attitudes towards animals I have seen. I don't entirely blame the writers, because I would hazard a guess that they, like most bureaucrats, are utilitarians (believing in the greatest good for the greatest number). Such a detached view of the suffering of sentient beings almost follows by cold hard logic from this ethic, and this utilitarian 'emotional death' is one of the key reasons I find that the Principle of Goodness offers a more spiritual and caring way to approach these difficult questions.

Anyway, apologies for spending time critiquing the EEA's writing style, but this is a site, above all, on building a peace legacy for our descendants. A pretty sorry legacy it will be, IMHO, if the frigid attitude of the EEA is the one we teach our children.

So let's get down to it. I'll investigate these specific claims:

  • My green friend said not a bird corpse was to be found on her visit to the wind farm, but the article says "Bernd Koop, based on monitoring studies conducted in Holland by Winkelman, estimated there would be 60,000 to 100,000 bird collisions per 1,000 megawatt installed capacity in his country."
  • My friend said the blades spin ever so slowly that they could not possibly take a bird by surprise and hit it, but the article above says they spin at "over 200 miles per hour";

Why am I contrasting my friend's statements with the contrary allegations in this way? Because I have one of those sneaky suspicions that both my friend and the shocking accusations against wind farms will be correct. And I think I know why. So let's start with that EEA report:

Collision risk. Birds and bats may collide with rotors, towers and nacelles or with associated structures such as cables and meteorological masts. There is also evidence of birds being hit by the wake behind the sweeping rotor blades (Winkelman, 1992). With some notable exceptions the majority of studies have recorded relatively low levels of collision mortality but most were based only on finding corpses — a method that may underestimate mortality

 Hmmm. Let's see what "relatively low" means to the EEA:

... the history of modern wind turbines is short and only a single study has been sufficiently comprehensive and long-lasting to produce a thorough analysis of population impacts. This is the study of the golden eagle in the Altamont Pass Wind Resource Area in the Coast Range Mountains of California. Here, wind energy development began in the 1970s and when the number of wind turbines peaked in 1993, 7 300 turbines were operational within an area of about 150 km2 . An estimated 35 000–100 000 birds, 1 500–2 300 of them golden eagles, have been killed by collision here during the past two decades ... the golden eagle population in the Altamont region is declining and that at least part of this decline is due to wind farm mortality ...

As we have been told these studies are probably underestimating, I don't think it can be unreasonable to use, say, 73,000, as an estimate of bird deaths from this one wind farm. That's 10 per turbine in twenty years, or 0.5 per turbine per year.

Now I think it is becoming clear how my green friend and the wind farm critics can both be telling the truth. A bird killed by a turbine will likely be scavenged within a day or two. If you pay a single visit to a wind farm, you'll have to actually walk up to the bases of about 200 turbines to get around a fifty-fifty chance of seeing one dead bird (assuming you don't overlook it in the grass, or it didn't walk away injured and in great pain to die a slow death under cover somewhere).

The problem here is the incredibly low power density of wind farms. A single coal-fired plant will use far less land, produce more power, cost less, and last three times longer. So the entire caboodle needed to power a large city from wind occupies a huge tract of land and needs vast numbers of turbines. The consequence is that a very low probability of disaster for one turbine results in a massive total carnage. Also, so many turbines are needed that costs are prohibitive to install bird warning devices on each and every one.

Looking further in the EEA report, we find higher estimates for bird deaths:

At a few wind farms fatality rates of more than 50 birds per turbine were recorded annually. High-risk farms were either placed on mountain ridges, where chiefly raptors were killed, or near wetlands, where gulls were the main victims.

So the death rate is very much higher where wind farms are the most useful? It's getting worse and worse. But let's take that 50 per turbine figure: That still means a bird is killed by a single turbine only every seven days or so. Anyone visiting a wind farm is unlikely to ever see a dead bird, despite what any real lover of our nonhuman friends must surely consider an horrific death toll. Elsewhere the report tells us various other estimates for bird collisions; it tells us the shocking finding that bat deaths (between 0 and 50 per turbine per year) probably outnumber bird deaths - yet surely there are far more birds than bats? These figures, IMHO, represent shame on the human race for producing such a monstrous killing system - and being so very proud of it. Incidentally the report also tells us other unexpected dangers from these systems, such as damage to the hearing of dolphins and seals.

Let's pursue the total deaths question. Obviously there is no real data available to answer this accurately, but in light of the above, I think it must surely be conservative to use twenty bird+bat deaths per turbine per year. So how many turbines are there? Surprisingly, this is a hard question to find an answer for on the web. But we can make an estimate. On page 5, the report tells us "At the end of 2008, there were 65 GW of wind power capacity installed in the EU." Page 15 tells us that current average turbine power is "1—1.5MW". (Don't they know the correct answer?) Anyway, let's take 1.25MW as the average across the EU. That gives us something like 52,000 turbines. At 20 deaths each, that gives us 1,040,000 deaths per year for the EU. We are told on page 8 that current wind energy represents 3.7% of total energy use, and it is projected to expand to 12%. Then the death rate will be over 3.3 million (and this estimate could easily be many times too small, but is very unlikely to be too large).

I think it is easy to see how a sincere and caring investigator visiting a wind farm will not notice any animal deaths, whilst the hidden death toll is horrific. But why do these killing machines look so safe? What about the blade speed? Remember, my green friend says they spin ever so slowly, certainly far slower than a bird, and so they just can't do any damage. The article about bird deaths, however, said the ends of the blades move at 200 miles/hour (and yes, that can definitely kill any bird on the planet). To answer this question I'll go to the web site of a wind turbine supplier, GE Energy.

According to their specs, a typical wind turbine (picking an average-looking one from the list here) has a diameter of 77m (this is in the range given in the EEA report for current turbines) and a maximum speed of 20.4 rpm. This means the circumference is pi times the diameter, or 241.9m. The outer edge of the blade will sweep out this distance 20.4 times per minute, or 1,224 times per hour, covering a distance of 296km/hour, or 183 miles/hour. That is the result for the very first turbine I investigated. I think we can say that blade speeds of approximately 200 miles/hour are confirmed from an authoritative source. So how can a caring and honest observer fail to see this vicious killer speed?

Here's what I think is going on. It so happens I have had a long-standing interest in model railways, and at times I have had models in what is called OO gauge - 4mm model length for each real-life foot - or 1 in 76. I have at times calculated the speed I should run a train to make it go at a scale 80 miles per hour. 80 miles is 128 kilometres, which is, scaled 1:76, about 46 centimetres per second. Now 80 mph is fast, but a model train running at 46 centimetres/second seems to be dawdling. Onlookers always say "Speed it up! Make it go at a realistic speed!"

Why the complaint? Because, surprisingly, to get similar dynamic effects from a model as from the full-scale original, speeds do not scale in proportion to the lengths. There is a nice description of this effect here. One estimate of the correct way to scale speeds is to divide by the square root of the scale proportion rather than by the proportion itself. In the model railway case, this would give a speed of about 4 metres per second. Now that looks fast! And so is 80mph.

What is this to do with wind turbines? I think the problem comes when we see large objects from a distance. An 80-metre wind turbine way over there on that hill "looks like" a model with a size of maybe six inches. Now that turbine is rotating at 20 revs per minute, or one rev per three seconds. Now hold out your hand and sweep out a six-inch circle, taking three seconds to do so. Easy, isn't it? Nice and slow, even lazy going. Another time I noticed this effect was when I took a parachute jump. From way up there, the world looks slow, the cars on the highway look like slow-moving toys, the descent looks dead easy, but just as the ground approaches, everything speeds up and you suddenly realise just how fast everything really is going. But from a distance, you just can't "get the feeling" for it.

So that's my guess: I think wind farms look safe because our minds unconsciously scale them using a dynamically incorrect formula: we scale them in proportion to their linear scales (in fact we have no choice, that's what we are seeing with our eyes), but a square root scale would be more accurate. The result is we just don't 'see' how violent and deadly they are - one 300km/h blade per second slicing through the air. It is a wonder that far more birds aren't being killed.

But getting back to my green friend again, she has a small wind turbine on her roof, and tells me it provides good backup power for her solar generators when they go offline during the evening, but that wind, alone, doesn't provide full power for their home. Unlike the big turbines, hers, about a metre in diameter, makes a loud buzz as it turns, much like a noisy desk fan. That will guarentee that it never kills a bird - they'll hear it long before they see it. BTW, I think one other important point arises here: wind power may very well be useful and safe on a small-scale 'local' level, whilst being a dangerous monstrosity on a large scale. I imagine a small turbine like hers, with a circular rim to provide an obvious outline for flying animals, and quieter blades, installed on each home: no danger to wildlife, and relief for the power grid.

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Re: Wind Farms: Do they kill birds?

I thought that you might like the latest update on this: